Direct positive silver halide emulsions containing thallium salt and mercury salt

ABSTRACT

Direct positive photographic silver halide emulsions containing a monovalent thallium salt and/or a monovalent or divalent mercury salt.

United States Patent Inventor Oskar Riester Leverkusen, Germany Appl. No. 790,043

Filed Jan. 9, 1969 Patented Nov. 16, 1971 Assignee Agfa-Gevaert Aktiengesellschaft Leverkusen, Germany DIRECT POSITIVE SILVER HALIDE EMULSIONS CONTAINING TI-IALLIUM SALT AND MERCURY SALT 6 Claims, 7 Drawing Figs.

U.S. Cl 96/108, 96/64, 96/110 Int. Cl G03c l/28 Field of Search 96/108, 64, 1 l0 [56] References Cited UNITED STATES PATENTS 2,728,664 12/1955 Carroll et a1 96/110 3,178,282 4/1965 Luckey et a1. 96/64 X FOREIGN PATENTS 658,434 10/1951 Great Britain 96/108 Primary Examiner-Norman G. Torchin Assistant ExaminerWon l-I. Louie, .lr.

Attorneys-Walter C. Kehm, Samson B. Leavitt, Geroge L.

Tone and Morton Friedman ABSTRACT: Direct positive photographic silver halide emulsions containing a monovalent thallium salt and/or a monovalent or divalent mercury salt.

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LOG Ii DENSITY IN v/ ml '1 (1/4 .OSKAR RIEST ER ATTORNEY DIRECT POSITIVE SILVER HALIDE EMULSIONS CONTAINING THALLIUM SALT AND MERCURY SALT The present invention relates to photographic silver halide emulsions for the production of direct positive pictures which are improved with regard to speed, gradation and contrast by addition of compounds of monovalent thallium and of Hg.

The addition of salts of monovalent thallium to photographic silver halide emulsions has been known for a long time. The effect of the thallium compound consists in strongly increasing the speed and in certain cases also in improving the contrast. Practical use was not possible up to the present time since as a result of the increase in the speed, the fogging of the emulsion was also favored. This disadvantage could not be eliminated heretofore. Accordingly, there was a considerable bias against the use of thallium salts in direct positive emulsions.

The use of salts of monovalent or divalent mercury has also been investigated. They show a stabilizing effect which to be sure is frequently accompanied by a reduction in speed and a flattening of the gradation.

Up to now, the speed of silver halide emulsions which tend towards solarization and are therefore suitable for the production of direct positive pictures, has been increased by adding spectral sensitizers. By this measure, a considerable improvement in this respect has already been obtained. In general however the contrast and the gradation of such a silver halide emulsion are unfavorable affected by the addition of spectral sensitizers, i.e. the contrast is reduced and the gradation flattened.

The object of the present invention is to develop silver halide emulsions for the production of direct positive pictures which assure a steep gradation curve and high contrast together with sufficient speed.

It has now been found that for the production of direct positive pictures by the solarization principle there are suitable photographic silver halide emulsions which contain monovalent thallium salts or salts of monovalent or divalent mercury, possibly-in accordance with the preferred embodiment-combined with each other.

With the emulsions of the invention which have a steep gradation there are obtained direct positive pictures of excellent contrast. Another advantage of these emulsions is a considerably reduced tendency towards fogging, which is also obtained by the addition of thallium and mercury salts.

The emulsions of the invention are superior specifically in the last mentioned respect in known direct positive emulsions in which the contrast and the gradation was obtained by a simple increase in the emulsion thickness. Such emulsions are however detrimental for economic reason due to the increased consumption of silver. Furthermore the clarity is decisively impaired by an increase in the basic fog.

The added amounts of thallous salts can vary within wide limits. in general, quantities of between 50 mg. and 2 g. and preferably 0.1 and 0.5 g. per kg. of emulsion are sufficient. The thallium salts are best added in dissolved form as an aqueous solution at any desired time before the pouring of the silver halide emulsion.

lf Hg salts are added, then the speed in particular increases and the gradation is made steeper, but the maximum density is less affected.

In accordance with the preferred embodiment, the thallium salts are used together with salts of monovalent or divalent mercury, for instance l-igCl mercuric acetate, mercuric cya nide, H,NO Hg(NO l-lg Cl (dissolved in pyridine), etc. The speed is thereby considerably increased without the other advantages being impaired. The added quantities of the mercury salts can also vary within wide limits. The optimum quantitles of addition are between about l/20th and one-half of the quantity of thallium salt, i.e. from to 100 mg./kg. emulsion.

For the preparation of the emulsions of the invention the customary direct positive emulsions are suitable. As photosensitive silver halides they can contain silver chloride and/or silver bromides possibly mixed with silver iodide. There are preferred emulsions which contain substantially silver bromide possibly together with up to 10 mol percent silver iodide. The emulsions of the invention contain about 20 to 3. silver in the form of silver halides per kg. of poured solution. Quantities of about 40 g. of silver per kg. are preferred. Chemical fogging is brought about in the customary manner for instance by means of ammonia with excess silver nitrate at elevated temperature. The production of such emulsions is described in German Pat. Nos. 606,392 and 642,222 or in British Pat. Nos. 581,773 and 655,009.

The emulsion can furthermore also contain the other customary additions such as wetting agents, spectral sensitizers, hardeners, stabilizers, color couplers, antiyellow fog agents as well as density-increasing agents, screen colorants, etc.

As spectral sensitizers, there are suitable for instance the lndol dyestuffs known from German Pat. Nos. 1,008,118 or l,l53,246. There can furthermore be employed 4,4-bisthiazolmonomethincyanins or dior triphenylmethane dyestuffs of German Patents (A 54,235 lXa/57b), (A 55,427 lXa/57b) or (A56,656 lXa/57b).

EXAMPLE 1 A direct positive silver bromide gelatin emulsion which contains 2.5 mol percent silver iodide is prepared in customary manner. it is chemically fogged with ammonia in the presence of an excess of silver nitrate at higher temperatures of about 50 C. The manner of operation of the emulsion is based on the solarization principle.

To 1 liter of this emulsion (silver halide content 0.4 mol) there are added at 40 C. 5 ml. of a 5 percent aqueous solution of thallous sulfate. Thereupon dispersing is effected for 20 minutes at 40 C.

A transparent cellulose acetate support is coated with the emulsion in the customary manner and dried. Thereupon, it is exposed with white light in an ordinary sensitometer behind a gray step wedge. The exposed emulsion is developed for 5 minutes at 20 C. with a development bath of the following composition.

p-methylaminophenol-3.5 g.

sodium sulfite sicc.60.0 g.

hydroquinone-9.0 g.

soda sicc.40.0 g.

potassium bromide-3.5 g.

and filled up with water to 1,000 ml.

The developed sample is treated further in the customary manner and dried.

As comparison, the sample of the same emulsion but without addition of the thallous salt, but otherwise treated identically, was tested.

The results of the sensitometric evaluation of the two samples is shown in the accompanying FIG. 1.

In the diagram, the densities are plotted on the ordinate axis and the intensity of exposure in log (l.t) on the abscissa axis. Curve 1 corresponds to the comparative specimen and curve 2 to the emulsion of the invention (250 g. thallous sulfate per liter). By the addition of the thallium salt, the maximum density has been increased from 2.2 to 2.8; at the same time, the fog is reduced from 0.82 to 0.63. The gradation is considerably steeper.

EXAMPLE 2 A direct positive silver halide gelatin emulsion which was prepared in the manner described in example 1, but with a silver iodide content of 4 mol percent is divided into 3 parts.

Sample 1: Without further additions, as comparative sample.

Sample 2: 252 mg. of thallous sulfate (0.5 10 ''mol) and 13.5 mg. of murcuric chloride sulfate 0.5 '10' 5 mol) are added per kg. of emulsion.

Sample 3: The same quantity of thallous sulfate as in exampie 2 but 67.5 mg. mercuric chloride (2.5- 10 mol) are added.

EXAMPLE 3 The direct positive silver-bromideI-Iiodide-gelatin emulsion described in example 1 is divided into two parts:

Sample 1: 45 mg./kg. of the spectral sensitizer of the following formula described in US. Pat. No. 1,153,246 are added:

cg, /CH3 C-CH=CH l CH 01 l o t CH CH; V 3

Sample 2: The same quantity of the above-mentioned spectral sensitizer and in addition 250 mg. of thallous sulfate per kg. of emulsion are added.

The further treatment is the same as described in example 1.

The sensitometric evaluation leads to the curves of FIG. 3 in which curve 1 corresponds to sample 1 and curve 2 to sample 2. The improvement in the maximum density and in the fog as well as the increase in the steepness of the gradation is clearly noticeable.

EXAMPLE 4 The direct positive silver-bromide-iodide-gelatin emulsion of example 2 is divided into four parts.

Sample 1: 45 mg. of the spectral sensitizer of the following formula are added.

Sample 2: In addition to the same quantity of spectral sensitizer as in Sample 1, 252 mg. of thallous sulfate are also added.

Sample 3: In addition to the same quantity of the spectral sensitizer of Sample 1, 27 mg. mercuric chloride are added.

Sample 4: There are added 45 mg. of the spectral sensitizer of Sample 1, 252 mg. of thallous sulfate and 27 mg. of mercuric chloride.

The spectral sensitizer sensitizes with a maximum in the orange-red spectral region.

The further treatment is the same as described in example l.

The sensitometric evaluation leads to the curves of FIG. 4.

The curves are numbered in the same manner as the abovementioned samples.

It can clearly be seen that the addition of thallous sulfate to the spectral sensitized emulsion produces an increase in speed, in steepness of gradation, and in the maximum density. This can be noted from curves 2 and 4. By the further addition of mercuric chloride, the speed which is shown by curve 4 is increased about 4 times, in addition to a further improvement of the fog. The addition by itself of mercuric chloride (see Curve 3) to be sure also leads to a certain improvement but the increase in steepness of the gradation is insufficient as is also the improvement in the maximum density.

EXAMPLE 5 s 4 m can), clot Samples 2 to 4 are spectrally sensitized in the same manner and treated with increasing quantities of thallous sulfate (300, 450 and 600 mg./kg. of emulsion The further treatment is the same as described in example 1 The result of the sensitometric examination is shown in FIG. 5. The increase in the steepness of the gradation on basis of the increase in the concentration of the thallium salt is clearly visible. The same applies to the increase in the maximum density.

In FIG. 6, there is shown in the same manner the sensitometric behavior of the emulsions after storage for several days in a tropical cabinet. The advantageous effect of the additions of thallous sulfate is fully retained. The storage conditions were 20 C. and percent relative humidity.

EXAMPLE 6 The direct positive emulsion of example 2 is treated with 45 mg./kg. ofsensitizer of the following formula:

and per kg. of emulsion with 10 g. of the blue-green coupler ioxy-naphthaline-2-carboylamine [2- l '(methylstea rylamino)benzene-4'-sulfonic acid-sodium salt]. Thereupon the emulsion is divided into 4 parts.

Sample 1 serves as comparative sample without further additions. Samples 2 to 4 are treated with increasing quantities of thallous sulfate 150,300 and 450 mg./kg. The further treatment is the same as described in example 1. The sensitometric evaluation leads to the curves of FIG. 7. The curves are numbered in the same manner as the samples indicated above. The increase in steepness of the gradation, the gain in speed and the strong increase in the maximum density can clearly be noted. The substantial improvement result- Iclaim: 1. A direct positive photographic silver halide emulsion containing a (salt selected from the group consisting of) TABLE 1 monovalcnt thallium salt and (monovalent and divalent) a Relative m rcury salt. Sensitivity 1-. An emulsion according to claim 1 wherein, (in addition Max. 0.3 Y to a thallium salt, there is also included a divalent) the mercu- Fog 6 density over fog ry Salt is divalem ing from thallium and mercury salts can also be noted from the sta l 3. An emulsion according to claim 1 wherein the quantity of mercury salt amounts to one-twentieth to one-half the weight 4. An emulsion according to claim 1 wherein a thallium salt is present in amounts from 50 mg. to 2 g. per kg. of the emul- 5. An emulsion according to claim 1 wherein the silver halide is silver bromide containing a minor proportion of silver 6. An emulsion according to claim 1 wherein the mercury v t L m l t a n S 8 W l m a W u V i o l m n m m m a .m n .l t f .m m m O S .l S 5 0 S .l 2 2 0050 00 00 500 Hwy 90g 0505 1mm an an m n ma 2 H mm 1 nu muvv Rm 0 e S 7504 93 76 9.05 %041 2232 22 22 &4; e d 4274 84 66 025 5 5005 I 4620 1332 31 12 334 342 09 8 9- 3on0 1 0 m Mwwfi HM 0 0 0 0 0 0 0 & 0 00 F 0 0 0 0 TABLE 2 .i w n fixfifr W mmm mmmImIm :Tmmmmmmmm m a as a m m w m mmm "m immwyam t fliw imaa mm 1m mmmm i is s. h n ums n m HHHHmHH HHmHH H messaeesfisssiss em mmmmmmmnmmmmm m omwnu an mm mm g 

2. An emulsion according to claim 1 wherein (, in addition to a thallium salt, there is also included a divalent) the mercury salt is divalent.
 3. An emulsion according to claim 1 wherein the quantity of mercury salt amounts to one-twentieth to one-half the weight of the thallium salt.
 4. An emulsion according to claim 1 wherein a thallium salt is present in amounts from 50 mg. to 2 g. per kg. of the emulsion.
 5. An emulsion according to claim 1 wherein the silver halide is silver bromide containing a minor proportion of silver iodide.
 6. An emulsion according to claim 1 wherein the mercury salt is monovalent. 